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Proper targeting and activity of a nonfunctioning thyroid-stimulating hormone receptor (TSHr) combining an

Patrizia Agretti1, Giuseppina De Marco, Paola Collecchi

  • 1Medicina del Lavoro, Università di Pisa, Pisa, Italy.

European Journal of Biochemistry
|September 3, 2003
PubMed

Insights

Combining activating and inactivating mutations in the thyroid-stimulating hormone receptor (TSHr) reveals complex signaling behaviors. Unexpectedly, a double mutant with an inactivating mutation gained constitutive activity, suggesting altered cellular trafficking.

Area of Science:

  • Endocrinology
  • Molecular Biology
  • Receptor Signaling

Background:

  • Activating thyroid-stimulating hormone receptor (TSHr) mutations cause toxic adenomas.
  • Inactivating TSHr mutations lead to congenital hypothyroidism.

Purpose of the Study:

  • To investigate the functional consequences of combining activating and inactivating TSHr mutations.
  • To explore how combined mutations affect receptor signaling pathways and cell surface expression.

Main Methods:

  • Constructing and expressing double TSHr mutants (T477I/P639S and I486M/P639S) in COS-7 cells.
  • Measuring cyclic AMP (cAMP) and inositol phosphate (IP) production.
  • Assessing cell surface expression using binding and fluorescence-activated cell scanning.

Main Results:

  • Dual activating mutations increased constitutive cAMP activity but not IP production, indicating differential G protein coupling.
  • A double mutant with an inactivating mutation (T477I) unexpectedly exhibited constitutive activity in both cAMP and IP pathways.
  • The inactivating T477I mutation facilitated cell surface expression of the TSHr when combined with an activating mutation.

Conclusions:

  • TSHr mutation combinations yield complex signaling outcomes, affecting distinct pathways differently.
  • An inactivating TSHr mutation can restore cell surface expression and confer constitutive activity when paired with an activating mutation.
  • These findings deepen the understanding of TSHr-mediated diseases and receptor regulation.

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